1. Field of the Invention
The present invention is directed to a method for achieving a flat magnetization loop in amorphous cores by a heat treatment, and in particular to such a method for treatment of cores for use in inductive components wound of amorphous ribbon.
2. Description of the Prior Art
As discussed in the periodical IEEE Transactions on Magnetics, September 1984, pages 1415-1456, different magnetization curves can be obtained in an iron rich amorphous alloy by means of a 5 hour heat treatment at a termperature between 425.degree. and 595.degree. C. Dependent on the selection of the temperature in the heat treatment, permeabilities of .mu..sub.r =700 up to a pre-magnetizing field strength of H.sub.c =15 A/cm, or a permeability of .mu..sub.r =200 up to a pre-magnetization field strength of H.sub.c =100 A/cm can be achieved.
An article by Ok and Morrish in Physical Review Vol. 23, (1981), pages 2257-2261 discloses a heat treatment for alloys with 40% iron and 40% nickel, wherein the alloy is exposed to a temperature between 375.degree. and 400.degree. C. for 10 hours. Iron rich alloys having 65% or 82% iron are respectively heat-treated for one hour or 20 minutes. Cystalline precipitations, predominantly at the surface of the ribbon, which cause a volume reduction at the surface, arise due to this heat treatment. As a consequence, compressive strains occur in the inside of the ribbon, resulting in a preferred magnetization direction perpendicular to the longitudinal (longest) direction of the ribbon in the amorphous core due to the positive magnetostriction of the iron rich alloy. This causes the remanence magnetization and the permeability to be reduced be the heat treatment, so that such heat-treated cores are suitable for inductive components using DC pre-magnetization.